EP2255085B1 - Stirling engine - Google Patents

Abstract

The invention relates to a Stirling engine (1) having at least one cylinder in which are arranged two pistons (6, 6') which move counter to one another, wherein each piston (6) is connected by means of a first connecting rod (7, 7') to an oscillating arm (8, 8') and the oscillating arm (8, 8') is connected by means of a second connecting rod (9, 9') to the crankshaft (10), characterized in that the oscillating arm (8, 8') is articulatedly connected at its first end to the second connecting rod (9, 9'), in that said oscillating arm (8, 8') is pivotably mounted at a second end on the cylinder housing (3), and in that the first connecting rod (7, 7') is articulatedly connected between the first and the second end.

Description

The invention relates to a Stirling engine with at least one cylinder, in which two mutually movable piston are arranged, each piston is connected via a first connecting rod with a rocker arm, and the rocker arm via a second connecting rod to the crankshaft.

A Stirling engine is a work machine in which heat is supplied from outside to a cylinder or discharged from a cylinder. It is possible to operate the machine as a motor, wherein a working medium is alternately cooled and heated in a cyclic process to produce mechanical work. Conversely, a Stirling engine can also be used as a chiller, in which heat is brought from a lower temperature level to a higher temperature level by the application of mechanical work. In the context of the present invention, it is possible to cover both fields of application.

It is known to form Stirling machines in the form of opposed-piston engines. In this case, in a common cylinder chamber or a cylinder arrangement, two pistons, a compression piston and an expansion piston, move against each other. Between the pistons of the regenerator and heat exchangers are arranged to alternately heat and cool the working gas during operation of the machine. The advantage of this design is that very large Überströmquerschnitte can be displayed, so that high efficiencies can be achieved even at low temperature differences.

From the GB 2 030 213 A is an internal combustion engine with an opposed piston construction known. The pistons are connected via a first connecting rod, a rocker arm and a second connecting rod with a crankshaft arranged laterally between the pistons. In the same way it is possible to form Stirling machines. With correspondingly long connecting rods, the time-distance diagram of the piston movement essentially corresponds to a sine curve. Due to the geometry of the crank mechanism, however, there is a deviation from a sinusoid, which is the greater, the shorter the connecting rod is in relation to the crankshaft pitch. In the case of the opposed-piston construction described above, this deviation causes the piston to move relatively quickly in the region of top dead center, while it remains relatively long in the region of bottom dead center. It turned out that this movement pattern is relatively unfavorable for Stirling machines, resulting in losses in efficiency.

In addition, the known solution has further disadvantages. The direct connection of flywheel and piston on the one hand, as well as the articulation at one end of the flywheel on the other hand act due to this geometry side forces on the piston. Since the pistons always run dry in a Stirling engine, in contrast to an internal combustion engine, these side forces have a very negative effect, in particular on the sealing behavior and the service life of the pistons.

Object of the present invention is to avoid the disadvantages described and to provide a Stirling machine, in which a high efficiency is achieved even at low temperature differences.

According to the invention, these objects are achieved in that the rocker arm is articulated at its first end to the connecting rod, that it is pivotally mounted at a second end on the cylinder housing, and that the first connecting rod is articulated between the first and the second end. Essential to the present. Invention is the fact that is achieved by the changed geometry of the crank mechanism now a longer residence time of the piston at top dead center with faster movement in the same area of bottom dead center. In this way it is possible to achieve higher efficiencies. Another advantage of the present invention is the way in which the forces are applied to the pistons.

As a result of this type of connection of the piston to the crankshaft, practically no lateral forces act on the piston, so that the realization of larger piston diameters and consequently a larger cylinder volume is made possible. A higher gas volume also means a higher efficiency.

In a preferred embodiment of the invention, the rocker arm has two sections which are aligned at an angle to each other, wherein preferably the first connecting rod is articulated to the longer section. This version of the rocker arm allows a particularly compact design of the Stirling engine.

In order to further reduce the lateral forces acting on the pistons, advantageously the end of the longer section of the oscillating lever has two extensions over which the oscillating lever is articulated to the cylinder housing.

In a particularly preferred embodiment of the invention, the rocker arm is made in one piece. As a result, the number of individual parts of the rocker arm is reduced, which in turn extends the life of the rocker arm and reduces its production costs.

A further increase in efficiency is achieved when the second connecting rod is made short, especially if its length is shorter than three times the Kurbelwellenkröpfung. The shorter the connecting rod, the greater the deviation from the sinusoidal course of the piston movement and the higher the efficiency of the Stirling engine according to the invention.

Usually, a Stirling engine has a heat exchanger which serves to cool or heat the gas in the cylinder space. An improved heat exchange, and thus a further improvement in the efficiency, is given when each piston is assigned its own heat exchanger, which are spaced from one another in the cylinder housing between the pistons.

Preferably, the heat exchanger on slats, which are made of aluminum and spaced from each other by embossed knobs. This form of heat exchanger has proved to be particularly favorable for the flow behavior of the gas. The production of the heat exchanger is very inexpensive especially if it has a rectangular or square shape.

Particularly advantageous for the efficiency of the Stirling engine according to the invention is when a regenerator is arranged between the heat exchangers. This consists of sieve-like, porous or sponge-like material insert has the task to absorb a portion of the heat of the hot gas flowing therethrough and store it to give this heat in turn to the cooled gas when it flows back in the opposite direction.

The gas used is preferably hydrogen; but it can also be used other gases or gas mixtures, such as helium or air. Hydrogen has the advantage of a large heat capacity and good heat transfer, which improves the efficiency of the Stirling engine, but is to be treated carefully due to its highly exothermic reaction with the air or with oxygen. Therefore, a preferred embodiment of the invention has a pressure-tight housing in which the cylinder is housed encapsulated together with the crank mechanism. Within this case, there is a strong overpressure, for example 30 bar, while in the cylinder, for example, pressures of 30 ± 5bar prevail. Thus, the seals of the cylinder, In particular, the piston seals, only withstand a pressure difference of 5 bar from the pressure prevailing in the housing overpressure, while the seal of 30 bar is taken against the ambient pressure of the housing seal. This seal of housing to ambient pressure is compared to sealing by moving parts extremely simple and inexpensive to obtain.

Fig. 1

eine Schrägansicht einer erfindungsgemäßen Stirlingmaschine;

Fig. 2

eine Schrägansicht der Stirlingmaschine aus Fig. 1 ohne Gehäuse;

Fig. 3

eine Schnittansicht der Stirlingmaschine aus Fig. 2 mit Wärmetauscher;

Fig. 4

eine Schrägansicht des Wärmetauschers aus Fig. 3;

Fig. 5

den Kurvenverlauf der Kolbenbewegung;

Fig. 6

eine weitere Ausführung der Erfindung in einer Ansicht von vorne;

Fig. 7

eine Schrägansicht der Stirlingmaschine aus Fig. 6; und

Fig. 8

eine weitere Schrägansicht der Rückseite der Stirlingmaschine aus Fig. 6.

In the following the invention will be explained in more detail with reference to a non-limiting embodiment with associated figures. Show:

Fig. 1

an oblique view of a Stirling engine according to the invention;

Fig. 2

an oblique view of the Stirling engine Fig. 1 without housing;

Fig. 3

a sectional view of the Stirling engine Fig. 2 with heat exchanger;

Fig. 4

an oblique view of the heat exchanger Fig. 3 ;

Fig. 5

the curve of the piston movement;

Fig. 6

a further embodiment of the invention in a front view;

Fig. 7

an oblique view of the Stirling engine Fig. 6 ; and

Fig. 8

another oblique view of the back of the Stirling engine Fig. 6 ,

As in Fig. 1 illustrated, the Stirling engine 1 according to the invention is housed in a motor housing 2 and has a cylinder housing 3, which is composed of two symmetrical cylinder halves 4, 4 '. These identical cylinder halves 4, 4 'are gas-tightly connected to one another via a connecting part 5.

According to the Fig. 2 and Fig. 3 is in each cylinder half 4, 4 'a piston 6, 6' movably arranged. The piston 6, 6 'is articulated via a first connecting rod 7 with a rocking lever 8, wherein the rocker arm 8 terminates in the illustrated embodiment of the invention at its piston end in two extensions 80, 81. About these extensions 80, 81 of the rocker arm 7 is pivotally mounted on the cylinder half 4.

The other end of the rocker arm 8 is connected to a second connecting rod 9, which in turn is coupled to a crankshaft 10, wherein the crankshaft 10 drives a generator 100.

The rocker arm 8, 8 'is integral with two sections 82, 82', 83, 83 ', which are arranged at an angle of approximately 90 ° to each other and act as lever arms carried out. At the shorter lever arm 82, 82 'of the rocker arm 8, 8' via the second connecting rod 9, 9 'with the crankshaft 10 is connected. The longer lever arm 83, 83 'is connected on the one hand with its end via the extensions 80, 80', 81, 81 'with the respective cylinder half 4, 4' and on the other hand via the first connecting rod 7, 7 'with the piston 6, 6' ,

Due to this design of the rocking lever 8, 8 'act due to the toggle kinematics virtually no lateral forces on the dry-running piston 6, 6', so that the life of the plain bearing is significantly extended. Furthermore, this also makes possible the use of a shorter piston skirt, which on the one hand reduces the weight of the piston 6, 6 'and on the other hand reduces the costs for the piston 6, 6'. In addition, the translation of the rocker arm 8, 8 'allows large piston forces and thus large piston diameter, which in turn can be used with improved flow behavior in the cylinder 3, a larger volume of gas. The most uniform possible flow behavior results in improved efficiency. Due to the small piston stroke - seen in relation to the piston cross section - reduces the relative speed of the bearings used, resulting in an extension of their life and a reduction in gas friction losses.

Each cylinder half 4, 4 'consists on the one hand of a region with a circular cross section, in which the piston 6, 6' is movable back and forth, and a region of quadrangular, preferably square cross section, which is provided for receiving a heat exchanger 11, 11 ' , Between the two heat exchangers 11, 11 ', a regenerator 12 is additionally arranged in the connecting part 5, which is usually made of a porous and / or sponge-like material and is used for the storage of heat.

A usable in the inventive Stirling engine 1 heat exchanger 11, the Fig. 4 be removed. This heat exchanger 11 consists of soldered together aluminum sheets 13, for example with the dimensions 140 x 40 x 0.2 mm, which are spaced apart by nubs 14 which are embossed into the sheet, for example with a height of 0.2 mm. Mitschlötete, inserted tubes cause additional heat flow between the media. Due to the rectangular shape of the heat exchanger its production is particularly simple and inexpensive. It has been shown that despite the circular cross-section of the pistons 6, 6 'is given a good flow, in particular when the area of the piston 6, 6 'corresponds to that of the rectangular inflow surface of the heat exchanger 11, 11'.

Due to the symmetrical structure of the cylinder halves 4, 4 'with their pistons 6, 6' and the associated heat exchangers 11, 11 'reduces the number of different components of the Stirling engine 1 and thus also the cost of production of the same. The compact design of the cylinder 3 is also advantageous for a hermetic seal, which is particularly important especially when hydrogen is used as working gas in the cylinders.

The piston movements within the Stirling engine 1 during operation thereof are shown in the diagram in FIG Fig. 5 shown.

The line designated by the reference numeral 21 describes the sinusoidal course of the piston movement of the so-called expansion piston 6, ie that piston which operates in the heated part of the Stirling engine 1. It can be clearly seen that the curve deviates from the ideal sine curve 20. In region A of top dead center, the curve is flatter, i. the piston remains longer at top dead center, while the curve in the area B of bottom dead center is steeper and thus remains shorter in this position. This distortion of the sinusoidal course of the piston movement can be significantly influenced by the length of the second connecting rods 9, 9 '. The shorter the second connecting rods 9, 9 'are made, the stronger the distortion. By this approach to a process running discontinuously in the theoretical ideal case, efficiencies can be achieved which are higher than those of the Stirling engines disclosed in the prior art.

As the bottom dead center here is the point at which the piston 6, 6 'has its greatest distance from the heat exchanger 11, 11', while at top dead center of the piston 6, 6 ', the heat exchanger 11, 11' almost touched.

The curve 22 of the compression piston 6 ', however, shows a flattening in the area B' of top dead center and a shorter residence time in the area A 'bottom dead center, thus has a co-behavior with the expansion piston 6. In addition to the offset by 180 ° movement, the piston movement is shifted by a phase angle of 72 ° (readable on the abscissa).

The line designated 25 describes the change in the total volume of the gas within the cylinder during the heating and cooling phase. If the expansion piston 6 is at bottom dead center, the gas is heated and its volume increases. Its volume is reduced by compression, when the expansion piston 6 approaches its upper dead center. At the same time, the gas is displaced into the cooling zone, cools down and its volume decreases while the compression piston 6 'moves upward.

Another embodiment of the invention is in the FIGS. 6 to 8 shown. In contrast to the embodiment described above, here the rocking lever 8 is executed without bending. The approximately sinusoidal course of the piston movement is achieved in that the second connecting rod 9 is substantially longer than the first connecting rod 7, which connects the rocker arm 8 to the piston 6 is formed. Likewise, the ratio of the two oscillating lever sections 82, 83 of the rocker arm 8 and the ratio of the length of the first connecting rod 7 to that of the second connecting rod 9 affect the piston profile.

The rocker arm 8 is articulated in this embodiment of the invention via a straight shoulder with bush 31 to the cylinder housing 3. Due to the straight design of the rocker arm 8, a more compact and easier-to-manufacture construction of the Stirling engine 1 according to the invention is achieved.

Also in this Stirling engine 1, each cylinder half 4, 4 'are each associated with a heat exchanger 11, 11' with a lamellar structure, wherein a regenerator 12 between the two heat exchangers 11, 11 'is arranged. The heat exchangers 11, 11 'are in this case constructed of a plurality of aluminum hollow chambers on the coolant side and corrugated fins on the gas side similar to a vehicle radiator.

It is understood that the invention is not limited to the embodiment described above. It has been found that the Stirling engine according to the invention is particularly suitable for use as a heat pump for energy-saving temperature control of a house by exploiting, for example, a solar system.

Claims (11)

1. A Stirling engine (1), comprising at least one cylinder in which two pistons (6, 6') are arranged which move counter to one another, with each piston (6, 6') being connected by means of a first connecting rod (7, 7') to an oscillating lever (8, 8'), and the oscillating lever (8, 8') is connected by means of a second connecting rod (9, 9') to the crankshaft (10), characterised in that the oscillating lever (8, 8') is connected in an articulated manner with its first end to the second connecting rod (9, 9'), it is pivotably mounted at its second end in the cylinder housing (3), and the first connecting rod (7, 7') is connected in an articulated manner between the first and second end.
2. A Stirling engine (1) according to claim 1, characterised in that the oscillating lever (8, 8') is arranged in a straight line, and the first connecting rod (7, 7') is connected in an articulated manner to the oscillating lever (8, 8'), through which the oscillating lever (8, 8') is subdivided into two sections (82, 83) which preferably have different lengths.
3. A Stirling engine (1) according to claim 1, characterised in that the oscillating lever (8, 8') comprises two sections (82, 82', 83, 83') which are arranged at an angle in relation to one another, with the first connecting rod (7, 7') being connected in an articulated manner to the longer section (83, 83').
4. A Stirling engine (1) according to one of the claims 1 to 3, characterised in that the end of the longer section (83, 83') comprises two projections (80, 80', 81, 81') through which the oscillating lever (8, 8') is connected in an articulated manner to the cylinder housing (3).
5. A Stirling engine (1) according to one of the claims 1 to 4, characterised in that the oscillating lever (8, 8') is provided with an integral arrangement.
6. A Stirling engine (1) according to one of the claims 3 to 5, characterised in that the second connecting rod (9, 9') is provided with a short arrangement, with the length of the second connecting rod (9, 9') preferably being shorter than three times the crank throw.
7. A Stirling engine (1) according to one of the claims 1 to 6, characterised in that each piston (6, 6') is associated with a separate heat exchanger (11, 11') which are arranged spaced from one another in the cylinder housing (3) between the pistons (6, 6').
8. A Stirling engine (1) according to claim 7, characterised in that the heat exchanger (11, 11') comprises ribs (13) which are made of aluminium and are spaced from one another via embossed knobs (14).
9. A Stirling engine (1) according to claim 7 or 8, characterised in that the heat exchanger (11, 11') has a rectangular or square shape.
10. A Stirling engine (1) according to one of the claims 7 to 9, characterised in that a regenerator (12) is arranged between the heat exchangers (11, 11').
11. A Stirling engine (1) according to one of the claims 1 to 10, characterised in that the cylinder (3) plus piston drive is arranged in an encapsulated manner.

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